Polyurethane PSA for sensitive surfaces

Abstract

Polyurethane-based pressure-sensitive adhesive which attaches strongly to polar plastic surfaces, smooth metal surfaces and glass, but which has weak, if any, adhesion to paper, paperboard or skin and is easily detachable without damaging surfaces during its removal, and is reusable. The adhesive comprises a polyurethane formed by reacting an aliphatic or alicyclic polyisocyanate having a functionality of equal to or less than three with a combination of diol and triol.

1. A pressure-sensitive adhesive comprising the product of the catalytic reaction of:
 a) at least one aliphatic or alicyclic polyisocyanate having a functionality of less than or equal to three, 
 b) a combination of at least one polypropylene glycol diol and at feast one polypropylene glycol triol, the ratio of the number of hydroxyl groups in the diol component to the number of hydroxyl groups in the triol component being less than 10 the ratio of the number of isocyanate groups to the total number of hydroxyl groups being between 0.8 and 1.15, the catalyst for the reaction consisting of or comprising a bismuth carboxylate or bismuth carboxylate derivative, and 
 the diols having a molecular weight of less than or equal to 1000 and the triols having a molecular weight greater than or equal to 1000. 
 
     
     
       2. Pressure-sensitive adhesive according to  claim 1 , wherein said at least one aliphatic or alicyclic polyisocyanates are diisocyanates. 
     
     
       3. Pressure-sensitive adhesive according to  claim 1  wherein said polyisocyanate is selected from the group consisting of butane 1,4-diisocyanate, tetramethoxybutane 1,4-diisocyanate, hexane ,1,6-diisocyanate, ethylene diisocyanate, 2,2,4-trimethylhexamethylene d iisocyanate, ethylethylene diisocyanate, dicyclohexylmethane diisocyanate, ,1,4-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclopentane, 1,2-diisocyanatocyclopentane, 1,2-diisocyanatocyolobutane, 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclo-hexane (isophorone diisocyanate), 1-methyl-2,4-diisocyanato-cyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane 1,6-diisocyanato-2,4,4-trimethylhexane, 5-isocyanato-1-(2-isocya natoeth-1-yl)-1,3,3-trimethylcyolohexane, 5-isocya nato-1-(3-isooyanatoprop-1-yl)-1,3,3-trimethylcyclohexane, 5-isocyanato-1-(4-isocyanatobut-1 -yl)-1,3,3-trimethylcyclohexane, 1-isocyanato-2-(3-isocyanatoprop-1-yl)cyclohexane, 1-isocyan ato-2-(2-isooyanatoeth-1-yl)cyclohexane, 2-heptyl-3,4-bis(9-isocyanatononyl)-1-pentylcyclohexane, norbornane diisocyanatomethyl, chlorinated aliphatic or alicyclic diisocyanates, brominated aliphatic or alicyclic diisocyanates, sulphur-containing aliphatic or alicyclic diisocyanates, phosphorus-containing aliphatic or alicyclic diisocyanate and derivatives thereof. 
     
     
       4. Pressure-sensitive adhesive according to  claim 1 , wherein at least one of said polypropylene glycols has originated from a DMC catalyzed preparation process. 
     
     
       5. Pressure-sensitive adhesive according to  claim 1 , wherein said at least one polypropylene glycol triol is prepared by DMC catalysis. 
     
     
       6. Pressure-sensitive adhesive according to  claim 1 , further comprising formulating ingredients selected from the group consisting of catalysts, ageing inhibitors (antioxidants), light stabilizers, UV absorbers and rheological additives. 
     
     
       7. Process for preparing the pressure-sensitive adhesive of  claim 1 , comprising
 a) charging a first vessel (A) with a premixed polypropylene glycol component comprising a combination of at least one polypropylene glycol dial and at least one polypropylene glycol triol and charging a second vessel (B) with an isocyanate component comprising at least one aliphatic or alicyclic polyisocyanate having a functionality of less than or equal to three, optionally also charging said first or second vessel, or both of said vessels, with one or more formulating ingredients selected from the group consisting of catalysts, ageing inhibitors (antioxidants), light stabilizers, UV absorbers and rheological additives, 
 b) conveying the polyol component and the isocyanate component via pumps through a mixing head or mixing tube of a multi-component mixing and metering unit, to mix them to form a reactive polyurethane composition, 
 c) applying the reactive polyurethane composition to a backing material, 
 d) passing the backing material coated with the reactive polyurethane composition applied thereto through a heating tunnel to cure the polyurethane composition to form a pressure-sensitive adhesive, 
 e) winding the backing material with the pressure-sensitive adhesive thereon up in a winding station. 
 
     
     
       8. Process according to  claim 7  wherein the preparation takes place without solvent. 
     
     
       9. Process according to  claim 7 , wherein the preparation takes place without addition of water. 
     
     
       10. A self-adhesive article comprising the pressure-sensitive adhesive of  claim 1 . 
     
     
       11. Method for the redetachable fastening without damage or residue of articles having sensitive surfaces, made from polar plastic, glass or metal which comprises fastening said articles with the pressure-sensitive adhesive of  claim 1 . 
     
     
       12. The pressure-sensitive adhesive of  claim 1 , wherein said ratio of the number of hydroxyl groups in the diol component to the number of hydroxyl groups in the triol component is between 0.2 and 5. 
     
     
       13. The pressure-sensitive adhesive of  claim 1 , wherein said ratio of the number of isocyanate groups to the total number of hydroxyl groups is between 0.95 and 1.05. 
     
     
       14. The pressure-sensitive adhesive of  claim 1 , wherein said ratio of the number of isocyanate groups to the total number of hydroxyl groups is between 1.0 and 1.05. 
     
     
       15. The pressure-sensitive adhesive of  claim 1 , wherein said molecular weight of said triols which are combined with said diols having a molecular weight of less than or equal to 1000 is equal to or greater than 3000. 
     
     
       16. The pressure-sensitive adhesive of  claim 2 , wherein said diisocyanates are diisocyanates having asymmetrical molecular structures. 
     
     
       17. The pressure-sensitive adhesive of  claim 3 , wherein said polyisocyanate is isophorone diisocyanate. 
     
     
       18. The process of  claim 7 , wherein said backing material to which said reactive polyurethane composition is applied is moving at constant speed during said application. 
     
     
       19. The method of  claim 11 , wherein said articles are selected from the group consisting of magazines, newspapers, books and letters.